Liquid fuel grid burner for vitiated air using auxiliary combustion air

ABSTRACT

A grid burner suitable for combustion of liquid fuel in vitiated air with auxiliary combustion air. Rows of auxiliary combustion air supply pipes support spaced fuel nozzles supplied by inner fuel pipes. Burner wings supported by the auxiliary air pipes include openings to direct vitiated air and auxiliary air into the combustion zone to provide the proper combustion and cooling patterns.

[ Oct. 22, 1974 United States Patent [191 Lambiris 3,051,464 8/1962 Yeoet al. 432/222 3,178,161 4/1965 Yeo et a1. 432/222 431/351 LIQUID FUELGRID BURNER FOR VITIATED AIR USING AUXILIARY COMBUSTION AIR Inventor:

3,632,286 1/1972 Kegan.... 3.64921 1 [75] Sortiris Lambiris, Andover,Mass.

Primary Examiner-John J. Camby Assistant Examiner-Henry C. YuenAttorney, Agent, or Firm-John F. Ahern; James W. Mitchell Appl. No.:338,993

[57] ABSTRACT A grid burner suitable for combustion of liquid fuel invitiated air with auxiliary combustion air. Rows of auxiliary combustionair supply pipes support spaced fuel nozzles supplied by inner fuelpipes. Burner wings supported by the auxiliary air pipes includeopenings vto direct vitiated air and auxiliary air into the combustionzone to provide the proper combustion and cooling patterns.

431/285 Int. F23q 9/00, F23m 9/02 [58] Field of Search................432/222; 60/39.?2 R; 431/350, 285, 351, 284; 110/8 A [56] ReferencesCited UNITED STATES PATENTS 2,796,118 6/1957 Parker et a1. 431/353 5 Cl4 D F. 2.799991 7/1957 Conrad 60/39.72 R aims, lawlng lgures Pmminum 19M3.843.309 sum 10; 2

LIQUID FUEL GRID BURNER FOR VITIATED AIR USING AUXILIARY COMBUSTION AIRBACKGROUND OF-THE INVENTION This invention relates generally to a gridburner suitable for burning liquid fuel to raise the temperature ofvitiated air. More particularly, the invention relates to an improveddesign of a liquid fuel burner employing auxiliary combustion air.

A grid burner employs a grid of fuel nozzles disposed transverselyacross a duct in order to raise the temperature of vitiated air or wasteheat gases'passing through the duct. A common use of a grid burner is toraise the temperature of gas turbine exhaust gases in order to generatesteam in a heat recovery steam generator. The gas turbine exhaustcontains sufficient oxygen-to support combustion, but improved burningwill result from proper introduction of v auxiliary combustionsupportingair. I

An example of a grid burner is shown in US. Pat. No. 3,632,286 issuedJan. 4, 1972 to R. E. Kegan and F. A. Underwood and assigned to thepresent assignee. That burner, adapted for burning both gas and liquidfuel, employed a fuel pipewithin another pipe, theoutside pipesupporting spaced fuel nozzles along its length and also supportingburner wingswith appropriately spaced holes to direct the flow of thevitiated air. That patent suggested introduction of pressurized air intothe outer pipe for atomization of liquid fuel. The present constructionconcerns an arrangement which is more suitable for introduction ofauxiliary combustion air at a relatively low pressure difference abovethe vitiated air pressure for support of combustion rather than for fuelatomization. Also the foregoing Kegan et al, burner required the removalof the entire assembly in order to correct anyproblem with the liquidfuel nozzles.

In a grid burner for burning vitiated air, the design should be such asto provide a low velocity sheltered region within the wings of theburner which is supplied with recirculating gases having enoughresidence time to ignite all of the liquid droplets and fragmentsinjected from the nozzle. Fuel pressure and geometry at the injectionpoint should be such that, at the recirculating regions, the injectedfuel can ignite, partially combust, and interact with the recirculatinggases replenishing their thermal capacity. Also portions of the fuelpenetrate into the unsheltered gas stream to complete its combustion inas uniform a manner as possible. For this reason, the arrangement ofports for admission of air to the sheltered region within the wings isextremely critical.

Accordingly, one object of the present invention is to provide a gridburner with an improved arrangement for admitting vitiated and auxiliarycombustion air to provide uniform combustion.

Another object of the invention is to providean improved liquid fuelnozzle assembly fora grid burner which can be easily removed forservicing.

Still another object of the invention is to provide an improved wingsupport and hole geometry for a liquid fuel grid burner.

DRAWING The invention both as toorganization and method of practice,together with further objects and advantages thereof, will best beunderstood by reference to the fol- FIG. 4 is a cross section throughthe burner element taken along lines IVIV of FIG. 3.

SUMMARY OF THE INVENTION Briefly stated, the invention is practiced byproviding a number of auxiliary air pipes extending across a duct, wingmembers supported on and spaced from the auxiliary air pipes, a numberof liquid fuel nozzles spaced on a liquid fuel supply pipe supportedwithin the air pipe and removable therefrom, a plurality of fuelinjection openings through the wing and air pipe, and a plurality ofvitiated air and auxiliary air admission openings through the wingmembers.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of thedrawing, the grid burner comprises a rectangular open frame 1 havingspaced cross members 2. Individual burner elements 3 are spaced acrossthe short dimension of frame 1. Each burner element 3 includesgutter-type flame holder wings 4 with fuel injection openings 5 arrangedin a grid of suitable spacing over the entire duct. Liquid fuel supplypipes 6 and auxiliary combustion air pipes 7 are connected to eachburner element. 3 on one side of the duct. A pilot ignition tube 8extends lengthwise along the duct. The entire base of frame 1 is coveredby grid of stainless steel wire mesh 9 to distribute the flow.

In one intended application of the present invention, frame 1 isinterposed in a duct carrying combustionsupporting exhaust gas from agas turbine and is used to heat the gas in a process known assupplementary firing as the gas travels toward aheat recovery steamgenerator. These details are not shown, but a typical system may be seenby reference to US. Pat. No. 3,443,550 issued to H. F. May and J. M.Kovacik on May'l3, 1969 and assigned to the present assignee.

Referring now to FIG. 2 of the drawing, each burner element 3 issupported in both side walls of frame 1 indicated at 10 and 10a. At sidewall 10a each burner elements auxiliary air pipe 13 rests and is free toslide there on a cantilevered support Ila rigidly attached to wall 10a.At side wall 10 each burner element 3 is supported at 10 within acantilevered support chamber 11 extending through wall 10. A firstremovable plate 12 is connected to an auxiliary air combustion pipe 13for removal of the entire burner element 3. A second flanged connectionat 14 permits removal of the liquid fuel supply pipe 6 and fuel nozzleassemblies. The wing members 4 are supported on spacer elements 15welded to the top of auxiliary air pipe 13. Wings 4 are in sections, oneend of each being welded to a spacer member 15 and the other being freeto slide thereon for thermal expansion and contraction.

Positioned'within auxiliary air pipe 13 is an assembly of short pipesegments 6a connected between fuel manifold support blocks 16. Eachsupport block 16 carries afuel nozzle 17 and a pair of locater pins 18.Each fuel nozzle 17 is positioned below an admission port 19 in thewing, thus forming a fuel injection point 5. The tops of fuel nozzles 17are short enough so that the entire fuel supply assembly of manifoldsl6, connecting segments 6a can be withdrawin longitudinally from theauxiliary air pipe 13, by breaking the flanged connection 14.

Referring now together to the plan view of FIG. 3 and the crosssectionof FIG. 4, the arrangement of elements will be describedin more detail.It is seen'that the cross section of each wing member 4 is roughly W-shaped, except that the central portion 20 of the W rests on spacermember and spaced above the auxiliary air pipe 13. The cross section ofthe wing member shows that the flat central portion bends down towardthe pipe 13 to form ashort inner leg portion 21, and then reversecurvature to form diverging outer leg portions 22. The latter form anincluded angle on the order of 90 degrees, although this will varysomewhat with the design. Inner legs 21, together with the sides of pipe13, form an elongated air supply passage 23 collecting vitiated air' oneither side of the pipe.

Vitiated air is admitted to a recirculating zone 24 between outer legs22 through a number of different types of passages. A first group ofelongated slots 25 are arranged along the inner leg portions 21 of thewings. A second group of spaced ports 26 are disposed approximatelymidway along the outer leg portions 22. A third group of passages 27 arespaced alongthe central portion 20 between the fuel injection points.

At the location of each fuel nozzle 17, and aligned with openings 19 inthe auxiliary air pipe, the wings are provided with enlarged openings28. Openings 28 are of a greater diameter than openings 19, and areproportioned with respect thereto so that a generally conical spaced isleft surrounding the spray conical angle 17a of fuel from the nozzle toadmit both vitiated air and auxiliary combustion air. Although the typeof nozzle 17 is not material to the present invention, suitable resultshave been obtained using a Delavan simplex spray nozzle providing asolid conical spray with an included angle on the order of 90.Primarycombustion takes place in a zone29 within the fuel spray angle. t

- It remains to note that the fuel manifold blocks 16 are beveled alongtheir lower edges at 30. By this means, together with locating pins 18,the fuel manifold is properly positioned inside the pipe so that nozzle17 is at the correct position and so that the fuel assembly can he slidout for servicing. If desired, a small leaf spring may be attached tothe underside of each manifold to maintain correct location and topermit easy withdrawal of the assembly.

OPERATION Operation of the invention will be understoodby reference toFIG. 4 of the drawing. Primary combustion of the fuel is enhanced byauxiliary air supplied at a slight pressure, on the order of 5 psi forexample, above the vitiated air pressure in the duct. This auxiliary airflows in annular sheaths through holes 19 surrounding the fuel sprayconical angle 17A as indicated by arrow 31, commencing penetration intothe fuel envelope with oxygen-rich air. This air flow is supplemented byannular sheaths of vitiated air flowing from passages 23 around the fuelspray cone, as indicated by flow arrow 32. This comprises the airsupply-at each of the fuel injection points 5 in the grid.

Additional vitiated air is supplied alongthe wings to provide coolingand a recirculating air flow. vitiated air from entry passages 23 entersthrough the elongated slots 25 and sweeps along the outer legs 22. Airalso enters from ports 26 in the outer legs and creates a recirculationof vitiated air and burning fuel in zone 24. Zone 24, it is understood,extends longitudinally along the burner, whereas'zones 29 are discreteor spaced along the burner above the fuel injection points.

The improved W-shape of the burner wing serves to provide a very usefuland simple means of providing the vitiated air supply passages 23. Thisenables the introduction of vitiated air through the space between thewing and the auxiliary combustion air pipe 13. At the fuel injectionpoints, the arrangement provides for an inner sheath of auxiliarycombustion air surrounding and penetrating the fuel spray cone and anouter sheath of vitiated air at a greater distance from the nozzle.

Since the fuel nozzle assembly is completely disposed within theauxiliary pipe, it can be removed in the event that nozzles 17 becomeplugged or require routine cleaning without thenecessity of removing theentire burner assembly. This can be done while the remaining burners inthe grid are in operation.

While there has been disclosed what is considered herein to be thepreferred embodimentof the invention, other modifications will occur tothose skilled in the art,.and it is desired to include in the appendedclaims all such modifications as fall within the true spirit and scopeof the invention.

What is claimed is: 1. In a grid burner having a plurality of spacedburner elements and adapted for flow of vitiated air past said burnerelements to be heated thereby, the combination of:

an auxiliary air pipe connected to a source of auxiliary combustionairat a pressure slightly above that of said vitiated air,

a fuel supply and nozzle assembly adapted to be withdrawn from saidauxiliary air pipe and comprising a plurality of spaced fuelnozzlesinterconnected by fuel supply pipe sections, the fuel nozzles disposedentirely within the auxiliary air pipe,

at least one elongated wing member supported by and spaced from saidauxiliary air pipe, said wing member being formed with inner legportions to provide elongated vitiated airsupply passages on either sideadjacent said auxiliary pipe and also having outwardly diverging outerleg portions providing a shielded circulation zone,

said pipe and said wing member each having openings concentric with anddownstream from each of said fuel nozzles to admit annular sheaths ofauxiliary and vitiated air-respectively around the fuel from saidnozzle.

2..The combination according to claim 1, wherein said wing member issubstantially W-shaped and wherein the inner legs of said W are providedwith a first group of longitudinally spaced vitiated air admissionopenings, whereby vitiated air can flow from said elongated viatiatedair supply passages through said first openings along the outer legs ofthe wing member.

3. The combination according to claim 2, wherein said wing membersinclude a second group of vitiated air admission .openings spacedsubstantially midway along the outer legs of said wing member.

mission openings disposed substatially midway on said outer legs.

5. The combination according to claim 1, wherein said fuel nozzleassembly includes a plurality of fuel manifolds furnished with locatingmeans to position the manifolds within the auxiliary air pipe, saidlocating means permitting withdrawal of the assembly longitudinallythrough said pipe.

UNITED STATES PATENT orwcs CERTEHQATE @i QQRREQ'HQN Patent No, 3,843,309Dat d October 22, 197

In t Sotiris Lambiris It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

The inv nt r's name should read:

-- Sotiria Lambiris gmd and gmaed this Twenty-seventh E December I 977[SEAL] Arrest:

RUTH C. MASON LUTRELLE F. PARKER Arresting Officer Acting Commissionerof Patents and Trademarks

1. In a grid burner having a plurality of spaced burner elements andadapted for flow of vitiated air past said burner elements to be heatedthereby, the combination of: an auxiliary air pipe connected to a sourceof auxiliary combustion air at a pressure slightly above that of saidvitiated air, a fuel supply and nozzle assembly adapted to be withdrawnfrom said auxiliary air pipe and comprising a plurality of spaced fuelnozzles interconnected by fuel supply pipe sections, the fuel nozzlesdisposed entirely within the auxiliary air pipe, at least one elongatedwing member supported by and spaced from said auxiliary air pipe, saidwing member being formed with inner leg portions to provide elongatedvitiated air supply passages on either side adjacent said auxiliary pipeand also having outwardly diverging outer leg portions providing ashielded circulation zone, said pipe and said wing member each havingopenings concentric with and downstream from each of said fuel nozzlesto admit annular sheaths of auxiliary and vitiated air respectivelyaround the fuel from said nozzle.
 2. The combination according to claim1, wherein said wing member is substantially W-shaped and wherein theinner legs of said W are provided with a first group of longitudinallyspaced vitiated air admission openings, whereby vitiated air can flowfrom said elongated viatiated air supply passages through said firstopenings along the outer legs of the wing member.
 3. The combinationaccording to claim 2, wherein said wing members include a second groupof vitiated air admission openings spaced substantially midway along theouter legs of said wing member.
 4. The combination according to claim 1,wherein said wing member is substantially W-shaped, the inner legs ofsaid W being provided with a first group of longitudinally spacedvitiated air admission openings, whereby vitiated air can flow from saidelongated vitiated air supply passages through said first openings alongthe outer legs of the wing member, and wherein said outer legs of saidwing member are provided with a second group of longitudinally spacedvitiated air admission openings disposed substatially midway on saidouter legs.
 5. The combination according to claim 1, wherein said fuelnozzle assembly includes a plurality of fuel manifolds furnished withlocating means to position the manifolds within the auxiliary air pipe,said locating means permitting withdrawal of the assembly longitudinallythrough said pipe.